The number of front wheel drive vehicles in the United States has grown from 6 million in 1975 to more than 30 million in 1987, and is expected to reach 84 million by 1995. All front wheel drive vehicles are equipped with constant velocity universal joints on the wheel axle. Constant velocity universal joints are disclosed in U.S. Pat. Nos. 4,177,654, 4,300,651, 4,476,950, and 4,634,402.
Constant velocity universal joints are susceptible to repair and replacement because of wear and tear through use and accident.
Use of the constant velocity universal joint causes the internal parts of the joint to wear and tear and eventually break down. The torque applied to the constant velocity universal joint is coupled from the output to the input through the ball bearings which attempt to move in a sideways direction, restrained by the grooves in the inner member and outer race member. Eventually friction between the ball bearing and the grooves, and deterioration of the parts caused by contaminants, begin to abrade the sides of the grooves. These factors allow for vertical and horizontal movement between the inner member and the outer enclosure and prohibit the free movement of the ball bearings forward and backward in the grooves. A break in the integrity of the protective rubber boot will often allow foreign particles into the grooves, increasing the rate of wear in the constant velocity universal joint. As mechanical play in the universal joint increases, vibration is induced in the operation of the vehicle. In severe cases of wear, an individual ball bearing may get caught in position, rather than freely rolling forward and backward as designed, resulting in joint seizure. Seizing of the constant velocity universal joint can cause damage to other components of the vehicle. Wearing of the internal components of the constant velocity universal joint eventually requires the replacement of the constant velocity universal joint. Complete replacement of the constant velocity universal joint is very expensive because of the cost of the precision machined components.
Moreover, a constant velocity universal joint is vulnerable to damage caused by loss of grease and/or intrusion of foreign materials into the protective rubber boot. If the rubber boot is ripped or pulls loose, the grease inside is quickly lost. The constant velocity universal joint can also be contaminated by dirt and water. Both occurrences result in the destruction of the internal components.
To remanufacture a worn or damaged constant velocity universal joint, it is known to grind the constant velocity universal joint components with surface grinding machines and rebuild the constant velocity universal joint with the ground components. A machinist manually works the individual machineable parts of the constant velocity universal joint, i.e. outer enclosure, grooves of the race members, and cage, by grinding with several different types of surface grinders and intermittently monitoring the diameter and/or other dimensions of the individual components. Monitoring of the grinding of the parts allows the machinist to change the mode of grinding if the monitored dimension deviates from a desired or optimum value. As a rule, the accuracy of the monitoring, and the grinding, depends upon the ability of the individual machinist operating the grinding machine to control the grinding machine. This manual grinding results in remanufactured constant velocity universal joint components whose dimensions may deviate from a desired value. This fact creates the need for large inventories of replacement parts, such as ball bearings of various sizes needed to compensate for and match the variations in the ground components, to insure the proper fit and operation of the reassembled constant velocity joint.
This method is prohibitively expensive and not often used, because it requires several different types of grinding machines, requires a skilled machinist with a thorough knowledge of constant velocity universal joints, and requires an extensive inventory of replacement parts of a variety of sizes.
It is also known to rebuild a constant velocity universal joint by replacing the worn or damaged parts and the protective rubber boot with a new boot and either new or salvaged internal replacement components. Usually the variations in internal dimensions which occurs in the original manufacture of the constant velocity universal joint, and is compensated for by the use of ball bearings of different sizes, is ignored during the rebuilding process. This results in either a tight fit or a loose fit between internal components of the constant velocity universal joint. Either case will usually cause premature wear or failure of the rebuilt constant velocity universal joint. An unacceptable high rate of premature wear or failure of constant velocity universal joints rebuilt using this method has caused the method to be expensive for the rebuilder and regarded poorly by automotive service agencies.